Cant merge partition back onto macintosh hd
I partitioned my macbook pro to download windows 10. I deleted windows 10 from the partition but it wont let me put it back on the macintosh hd partition. I have tried so many things but the minus sign is greyed out to merge the partitions. It is taking up a lot of space so I really want it back. What do I do?
MacBook Pro 13", macOS 10.15