Tooling is the name that has been assigned to this specific process. It involves a person using their index finger to make a smooth bond between the sealer and the surface. If done right, the result will be a neat finish that is without any gaps whatsoever.
There are little plastic tools available for this, but the good old finger method works best for me. It’s advisable to wear gloves while doing this is but in case you don’t, ensure that you clean the silicone remains on your hands after you are complete the task.
TOP TIP: half fill the bath with water before applying the new seal, it lowers the bath to the level it will be at when in use and forms a better seal.