You need to go to user settings program area/item and choose the lithium voltage which will switch the charger between lion, lipo, life. Basically a submenu. The charger is set up for nicd, pb, nimh, and lithium(but then 3 lithium chemistries within that).
If you only use LIPO then go to user settings and change the lithium to 3.7 volt (nominal). It will then display LIPO.
If you will use LIPO and LIFE or LION then choose the LIPO and then save some battery settings in the memory slots. You can then load the ones saved no matter what the current lithium voltages is active.
There should be a flow chart with the charger which will show you the additional lithium choice in user settings.
Hope this helps. It is confusing, I know.
If you don't have a manual. Look at page 10 and 11 etc. here.
https://astecmodels.co.uk/pdfs/Imax-B6%20manual.pdf