Unless you've got particular commitments at certain times of the day, I suggest simply forgetting about aiming for regular sleep patterns and simply sleeping when you really feel tired.
For example, I got up at about 0930 yesterday morning, after just one hour's sleep. I then stayed up until 0630 this morning, before sleeping for 13 hours until 1930 this evening. I might go to bed in a few hours time but it's possibly more likely that I'll stay up until the early hours of Monday morning. (I often stay up for anywhere between 20 and 50 hours). It seems to work for me!
For more conventional advice though, see these two pages from the HHS website:
https://www.nhs.uk/live-well/sleep-and-tiredness/how-to-get-to-sleep/
https://www.nhs.uk/every-mind-matters/mental-health-issues/sleep/