The first thing to do is to remove all the silicon sealant from the shower. I prefer to remove the shower enclosure from the tray and take it outside of the bathroom to clean and remove the sealant, this a time consuming job but if you do the job right the first time you won’t be doing it again in 6 months time, you can get silicon removers, which help but are quite expensive.
I now reposition the enclosure in the back on the tray, but do not re-fit the screws. I now put two lines of masking tape either side of the shower enclosure, I then carefully wedge the enclosure up off the tray to allow me to apply a line of silicon sealant between the lines of masking tape only along the edges, not at the corners we only want to seal these from the outside (see lower picture for reason).
We can now lower the enclosure back onto the tray re-fit the screws and remove excess silicon and tidy up the remaining. We now need to seal the corners from the outside, don’t seal on the inside of the corners, this will allow any water that has got between the sides and the corners to run out into the tray and not get trapped or seep out (see picture).
Finished Shower sealed with high quality silicon sealant.