Toilet has been leaking for a while (previous tenant didn't report the problem) and the skirting board is quite damaged. Need to know how to go about replacing it, including best way to remove it, assess damage behind it and then afix new skirting board.
Welcome to the Bunnings Workshop community @emcav. It's fantastic to have you join us and many thanks for your question.
Pictures of the damaged area would be fantastic in assisting our helpful members to give some great advice.
Depending on the extent of the damage you can scrape out the affected portion, apply Earl's 250ml Wood Hardener to stop the rot and then fill the area with builders bog. If the area has no structural integrity left then it would be a good idea to cut out a portion of the skirting board so you can inspect behind. Make sure you cut back far enough that you reach solid timber. You'll find an oscillating multi-tool can be very handy to get into those tight spaces and will make quick work of the project.