Bluetooth headphones connection issue

My iPhone won’t connect with my headphones, I’ve had them both for a couple of years with no issue.

But since last November, my phone refuses to connect and tells me to forget the device.

I forget the device, restart my phone and headset but then it doesn’t show in my list of devices to connect to. It takes a couple of days to show again. I can see both devices on other devices (eg they both show and connect to my tablet).

Both have up to date software.

Not sure what else to do but it is getting annoying as I like listening to it for my workouts. Any suggestions will be appreciated