dr_m.dawood, welcome to MR!
I don't know if it is possible to flash the Pocketbook firmware on a Foxit Slick reader. And if you won't get any knowing answers here maybe it is best to repeat your question in tne Netronix subforum (
https://www.mobileread.com/forums/forumdisplay.php?f=125).
What works is installing Open Inkpot on a Foxit Slick.