Hello @TitanNoob and welcome to the forum. I asked for solution for your problem why you can not assign onslaught for main attack and just got answer on your question today.
If u didn't find it yet I hope I can send a pic here
There you can change the auto attack you are using
BTW at that location are skeleton spawners what are a dope exp location if u just kill the 6 and relog
(https://cdn.discordapp.com/attachments/439575703231397898/678576959671894036/Screenshot_20200216_132147_com.dotemu.titanquest.jpg)
Now maybe your problem is related with your android device. I had experience where one game is working as it should on one Samsung phone which is newer but with lower performances, but same game is not working on 1 year older with better performances where game control are literally screwed and game is unplayable. So keep this on mind, sometimes problem can come from device.