How can I repair a Delta bathroom faucet with one handle?

To repair a Delta bathroom faucet with one handle, you can start by turning off the water supply to the faucet. Then, remove the handle and the cartridge inside the faucet. Inspect the cartridge for any damage or wear and replace it if necessary. Reassemble the faucet and turn the water supply back on to test for leaks. If the issue persists, you may need to contact a professional plumber for further assistance.