MIDI. If you have a MIDI controller or a keyboard you can just input a bass line via MIDI.

If you have a guitar you can record a single note bass line and either lower the recorded audio track one octave or use an audio to MIDI program to change it to MIDI. There are a number of programs that can do this conversion and some are free. I believe RealBand can do this if you are on a Windows system. You may have to edit the converted MIDI as there may be some mistakes, especially on the free conversion programs. Melodyne is the best program and with a monophonic line like most bass lines the least expensive can be used.

If you have non of the above you can step entry a MIDI bass track.

I hope this helps.

Back in my day the only time we started panic buying was when the bartender shouted "last call"!

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware