Any restriction for filing income tax returns

Dear Experts.,

I'm a accountant in a company. Having accounts knowledge and tally knowledge. In my company staffs and some my friends ask me for file their ITR... I filed their ITR returns with one of my friend's guide...

Can I file the ITR...?

In future any problem is to me...?

Can I start a accounts firm and also file Income Tax returns and GST returns...?

Please help to me and advice