Use plastic shims.
After you get the shims positioned, remove the toilet, replace the wax seal undeneath, and carefully put the toilet back over the shims Slowly press the toilet into place. Then caulk around the bottom to fill any gap and hide the shims.
After you get the shims positioned, remove the toilet, replace the wax seal undeneath, and carefully put the toilet back over the shims Slowly press the toilet into place. Then caulk around the bottom to fill any gap and hide the shims.