Upload text files to Onsong on 1st gen iPad without iTunes

I have a 1st gen iPad that I use for lyrics with an app called Onsong. It still works great and I put in a new battery. New versions of Onsong are subscription but the old version suits my needs so I have no reason to buy a new iPad. My new MacBook does not have iTunes. Is there a way to upload text Onsong files to the old iPad without iTunes?