We bought a 20kW UPS that is designed for 480V 3 phase. We are moving to a building that is only wired for 208V. Is there any way to convert 208 3phase to 480 volt 3 phase or will we need to scrap the UPS?

You can buy a transformer, and get a qualified electrician to install it.

No scrapping needed. Use a larger than 20 KVA 480 V to 208 volt Delta 3 phase transformer as a step up to supply the UPS.

Add the additional internal KVA of the UPS + 25%, and add that to the 20KVA output capacity of the UPS to size the transformer.

Be sure the transformer is K Rated. This is a beefier unit built to handle harmonics.

Take consideration of cooling , do not install the new transformer in an IT room.