Hi there can anyone help me. I am new to BIAB and am having trouble in placing chords to suit the melody of songs. Is some way to do this.

This is rooted, literally and figuratively, in music theory. If all that you have is a melody line to start with, it can be challenging. Have you ever taken a music theory class? If not then helping on this is going to take more than forum posts and time can help.

Welcome to the forums, Jackr :-)

So you happen to in luck, as BiaB can absolutely do this!

First, can I ask you if you have the melody line transcribed in any specific program, or are you starting from scratch (such that you want to input the melody line in BiaB and go from there)?

I ask this because I do what you describe by transcribing my melody in GuitarPro6 (which I find more comfortable to work with note entry-wise), and then port it over to BiaB.

it can absolutely do this.

A bit of understanding of music theory is really helpful.... but... it's easy to figure out rather quickly.

Besides music theory, although its helpful to know the circle of fifths, you can trust your ear too, not only for what sounds right, but also for what mood you are trying to create. You don't want to rush it though.

thanks for your reply. I play in a Gospel band but basically read guitar chords where they are above the lyrics. Is there any video tutorials on line that might help?

https://www.pgmusic.com/videos.bbwin.htm

Hope this is not too long winded:

You probably know, it usually works the other way around. While melody and accompanying chords,( sometimes called "comps,") go hand in hand, it is the chord progression that forms the foundation. The melody breathes life into the rhythmic chords and the progression. The good news is now we have Band in a Box to make life easier.
It is absolutely appropriate for you to develop a learning strategy. You are fortunate to be challenging yourself to learn the art of charting melodies. Many good musicians
pass over this skill area and content themselves to play the rhythms and progressions from, as you mention, lead sheets. A basic lead sheet consists of a poem with chords, such as we find on Chordie or any number of web sites. Now, you are expanding the information in a "poem with chords" treatment to include the bars, the structure. Taking notice of your Band in a Box interface, those are usually based on four bars per line, some variation of 4, 8, 12, 16, measures.
Plan on advancing to the use of full blown lead sheets.
A lead sheet as most often used consists of the lyrics, the bar count (usually four per line,) the treble staff (melody) and the bass line, or, basic chord structure. This leads into my urging you to map out your destination and strategy for reaching it now. You might find help from an experienced musician in the church.
For example, are you working in the 12 major keys? If you are playing from the hymnal, you probably will want a strategy that reflects this. Do you really need to bother with the bass clef? Those are questions to ask yourself. Again, Band in a Box is the perfect aid. It has automatic transposition to any key.

To answer your question about how to find the chords and changes in a melody, the basic rule is that the chords harmonize with the melody. A well written melody will take into account the projected accompaniment. The basic rule of harmony is the 1-4-5 progression.
If the key is Gmajor, it will probably start in G (the one) for two or three bars, then change to C or D, then back to G on bar five.
Mess around with it for a while and you'll begin to see the patterns. Knowing how to play rhythm, you are only a short step away already.
There are plenty of online tutorials that teach to this these questions. But, you have to sift through them.

If you are simply writing melodies without taking this into account, your battle will likely be uphill. Here, again, Band in a Box to the rescue. Keep in mind, "Chord and Lyric" type lead sheets can be ambiguous with respect to timing the individual notes. Once you have a good structure, though, you can adapt your melody to the structure. Not so easy the other way around.
I suggest you break out your Band in a Box, pick a key, then get to charting out some 12 bar blues or traditional folk until you get the hang of building backing tracks. And, keep asking questions. There are forum members who have worked through just about every problem you'll encounter. Hope this helps.