Cleaning up sound quality on interviews burned or imported from cassettes

I am working on a project which may become part of Storycorps. The project entails interviews recorded on cassettes, some by middle school students. I am new to Audiology and I find I need help ‘cleaning’ up the sound quality. These tapes have been sitting around since the early 2000’s and I have already ‘burned’ them or ‘imported’ them into Audiology. I have spent some time playing around with what the tutorial suggests but I think I need a bit (let’s say a lot!) more help. This is not music, just interviews. Any help or adivce would be greatly appreciated. Thank you, Linn