The water pressure in my master bath is dropping. Not sure what to do to fix it? We went on vacation and it was fine came back and the water pressure was much less. It is fine in the rest of the house. Thanks for your time hope you can help

Are any valves not fully open?

"are any valves not fully open?" Since they had good pressure when they left and less when they came back I doubt that it's a partially closed valve.
Are we talking about both cold and hot? The toilet as well as the lavatory and bath?
The first thing I would do is shut the water off and open up a faucet. Check the cartridge inlet ports for blockage and then turn the water back on to check the stream and flush out the line. If that clears up the faucet move on to the next one. Good luck, Tom