My advice is leave the tree ALONE

It depends on how much growing season you have left and where you are.

If it were springtime, I'd chop it back AT LEAST half way -- like to the top of the stake. But since it's getting toward the end of the growing season, any new growth may not have time to fully mature before you have to move the plant indoors.

But of course, that all depends on where you live and how you winter-over your plant.

With citrus ordered online, I find they are all super tall. Too tall for my taste. I always chop them way back. Typically I wait until the late winter or spring just before new growth begins. Early summer is good too.

Here's one I ordered that I ended up cutting way back to the top of the stake. Yes! All that beautiful new growth at the top went into compost (I actually did a few grafts from it).

Depending on where you are I agree that I would leave it alone. You mention it is an indoor mandarin, there is no difference between indoor and outdoor except where the grower chooses to grow their plant. If you're heading into fall with shorter days, then you don't want to encourage growth. You need to let the tree be and let it grow on its own. Then right before spring, I would cut it back by half. Wiring is also an option, but I wouldn't in this case.