Drill bit stuck in Hilti TE52

I'm assuming you've removed it before, so you know how? I've used Hilti hammer drills that either need a quick 1/8th counterclockwise turn to unlock it, and others like Bosch that are just pure quick release. Do first just make sure you understand how to remove the bit because it's sometimes not obvious and may be slightly different than how you insert it.

Typically an SDS bit can move front and back about 3/4" while being retained in the chuck. Or is it completely seized up?

Can you fill the chuck/drill bit interface with as much WD-40 as you can, then drill into steel at about 10% pushing strength and under 25% speed while retracting the chuck release while it's turning? You might need to use something slippery like a piece of plastic covered in mineral oil to hold it in while it's turning. The vibration should rattle the retaining mechanism free. Let the SDS drill bit bounce the hammer drill up and down as you do it.

I'm talking about quick release SDS chucks, but Hilti also makes some that work with normal round drill bits like a normal drill chuck. Those tips won't do anything for a regular drill chuck that's not an SDS style quick release. You could take a picture of it and post it here if you're unsure.

Basically find a way to make the tool vibrate itself enough to loosen it. I'm pretty sure you need the drill bit removed to completely remove and disassemble the chuck for cleaning/servicing, but not 100% positive on that model.

If it is a quick release SDS chuck, in the future be sure to apply a dab of lithium grease to the end of your drill bit every time you change it. Wipe off old grease and reapply every so often. Hilti makes a special pump applicator that's perfect to keep in your tool box, but just as long as you're using something it probably doesn't much matter. Just that basic pale yellow lithium grease is all that's in there as far as I can tell.