How can one reconcile the Sunnah of entering the restroom with the left foot first and the Sunnah of putting on footwear with the right foot first when entering the restroom?

The Sunnah is to present the right (foot/hand) in all matters of honor, and to present the left in all matters involving defilement or harm. If the sandals are outside the lavatory or can be taken out, then begin by putting on the right one when wearing them and entering the lavatory. However, if they cannot be taken out, then enter the lavatory with your left foot and place it on the sandal without wearing it, then bring in the right (foot) and wear the sandal with it first, then wear the sandal with the left (foot). In this way, you will have conformed to the Sunnah.