What are the recommended apps/ ways to find flatmates and flats?

Hi everyone, i’m in a sort of sticky situation, I moved to a horrible place( Luton) which I originally moved to temporarily as I wasn’t sure how hybrid my job would be, I’ve come to realize I don’t need to physically be in this place for my job and that I just need to be accessible to south bedfordshire like Leighton Buzzard, Luton, Dunstable, and that most my coworkers live in different areas and commute( I work in community NHS), I signed a lease with this accommodation and it’s a year lease but it does have a break clause ( I can leave as long as someone replaces me and I’m responsible to pay until a replacement comes along) I am looking into Hitchin, St Albans mainly as my coworkers recommend those places and live there and the commute isn’t bad for hybrid, it’s about 30-40 mins by car. How can I find decent flatmates and places? what apps do people use here? I have spareroom and open rent. Also any advice on how to work out the whole situation of initiating moving out/ finding a replacement/ moving into a new place at an appropriate time where i don’t pay double rent PS please no judgements or negative comments, I am new here and yes I know Luton sucks yes I know I shouldn’t have moved there but please be mindful of everyone’s personal circumstances, and I’m working on solutions moving forward. I appreciate your help and kindness :)