Opening a strong closed guard in the Gi is usually very tough.
You can either stand explosively and use both hands to push open the legs or you can pass from the knees.
For No Gi you can try this one:
Most Effective Way To Open Closed Guard in No Gi; Can’t Get Triangled From Here
In this video about breaking closed guard BJJ black belt Chew Jitsu shows 2 common mistakes he sees his white belts run into. They’re simple mistakes but ones that can make a huge difference when breaking closed guard in BJJ.
The staggered hand grip guard break is usually the first one most people learn and is the one he first shares in the video.
If you’re having trouble breaking closed guard. This video will help.
Sloth Jiu-Jitsu: you can be slow and unathletic and still kick butt in Jiu-Jitsu.