How can I cancel my employment visa after 6...

If you want to terminate the work contract and move to another company after the end of the probation period, if the work contract is for a limited period, it is not possible to terminate the current work contract and move to another company except after obtaining written approval from the employer to terminate the current work contract in order to avoid imposing a ban against you And prevent you from working inside the UAE for a year.
Here is the text of the UAE Labor Law, related to your inquiry
 (50 Article)
Unlawful interruption of work
If the foreign worker stops working, for an illegal reason, before the end of the contract term, no other work permit will be granted.
To join another job in the State in accordance with the provisions of this Decree-Law, for a period of one year from the date of discontinuation of work
The work, and it is not permissible for any other employer who is aware of this to use him or keep him in his service during that period.
The Ministry may exclude some occupational categories, skill levels, or employment from the provision of item (1) of these
Article, in accordance with the controls and procedures specified in the executive regulations of this Decree-Law.
The employer shall notify the Ministry of the incident of work interruption in accordance with the procedures specified by the regulation.
implementation of this Decree-Law.