Multi entry long time UAE visa for 90 days is a type of visa that allow to enter in UAE multiple times. This visa is....
https://www.visitsvisa.com/uae-visa/multi-entry-long-term-visa-90-days/

If you want to know about UAE Visa extension this website or link may be helpful. here you can know about process, fees, require documents....
https://www.visitsvisa.com/uae-visa/uae-visa-extension/