I ate fleishig then milchig unintensonally. What can I do?
According to Nesivos Hamishpat, a person who transgresses a rabbinic mitzvah inadvertantly does not need to do teshuvah for it. Although his opinion is not broadly accepted, eating milchig after fleishig is not a fully fledged rabbinic prohibition, and it originates more in custom than enactment. It is certainly obligatory to wait the required time between meaty and milky, but you don’t need to do anything after inadvertantly transgressing this obligation. The best course of ‘mending’ the deed would be use it to learn for the future–ensuring that you don’t make the same mistake in the future.