Please can I apply the new labour law to previous...

Kindly, could you clarify your question in details so we could help you legally better with pleasure.

We would like to inform you that in accordance with the UAE Labor Law, which regulates the nature of the contractual relationship between the worker and the employer, first, it must be noted that the probation period is an absolute right of the employer according to the law and he may terminate the services of the worker without prior warning or notice and without paying any compensation as stipulated in:
Article (37)
A worker may be employed on probation for a period not exceeding six months, during which the employer without notice or severance pay may terminate his services. A worker shall not be placed on probation more than once with the same employer. Where a worker successfully completes the period of probation and continues in employment, the said period shall be calculated as part of his period of service.