1 - get onto a website like Lyngsat or KingofSat (etc.) and select the satellite for which you want to find transponders (
@william-1's sat list might help) and find ones which ought to be "strong" in the UK
2 - on the SX88+, go into the menus, Installation, list of sats and select the one of interest - then click the Green F2 button on the remote to get you to the transponder list for that sat. and then click the Blue F3 button to get a pop-up menu where you can enter new transponder parameters
3 - From the sat transponder that you chose in "stage 1", enter the frequency, polarity (the default is Horizontal, so you change that if the transponder is "Vertical") and the bit rate, and then click on the "button" below to add that transponder to the transponder list for that sat.
3- Then use the (can't remember which, ATM) F button on the remote to go into Search Mode, and then start an actual search - that will probably take a minute or so, and result in a list of identified channels on the screen.
4- Exit that mode, and then, "with luck", and if the dish is correctly aimed at that sat, then the on-screen SS & SQ bars should then "light up" in red to show that you have got a signal - on the SX88 series, an SQ level of about 22% or higher should indicate that you might then be able to view receivable channels..
Tomorrow, I might comment further.