Hello,
I'm new to bonsai growing and am kindly seeking assistance. We have no idea how to re-pot or if we should attempt this in late August. It is overdue since I can see roots on the outside of the pot. It has been indoors until Spring. ( on humidity tray). It has recently been over watered...Ouch, and has a few leaves just starting to appear. What would you suggest? Thanks in advance.

It will do more bad than good to repot now.
Wait until the right time and look up how to repot under the 'How-To' section above