Assuming the property was placed in service before 2021, you never, under any circumstances and with no exceptions, change ownership percentage of an existing asset. No exceptions.
How you deal with this depends on how the change occurred, and in what direction. Do you own less than 50% now? More than 50%. How did your ownership percentage change? Did you sell some of it? Did you buy additional ownership share? Maybe it was gifted to you, or you inherited it? Precisely how you acquired an additional ownership percentage matters here. That will determine your cost basis of the additional ownership percentage, for depreciation purposes.
