Addressing and closing nonconformity regarding clause 7.2

Clause 7.2 requirements relate to the selection, verification and validation of methods. I cannot tell from your question what the specific nonconformity (NC) is. 

For all tests that your laboratory is accredited for you should have access to and be using the most recent standard methods or latest reviewed in-house methods. Then you should know what the performance requirements are to meet the purpose (use)of the test. Validation or verification activities must prove  that the parameters are suitable.

The nonconformance must be addressed according to your laboratory procedure. The specific problem statement is the crucial starting point, i.e. what should be in place and is not in place 
(a gap) or deviating from requirements. Then you should perform root cause analysis and find the correctable causes, that if addressed will resolve the nonconformance and stop it from reoccurring. Then select the appropriate actions and implement. Closing the NC will follow once it is verified that the action taken was effective.

The following may be of interest:

The ISO 17025 toolkit procedure Test and Calibration Method Procedure, along with two supporting documents Test Method Development, Verification and Validation Register and Test Method Development, Verification and Validation Record. The techniques for method validation are listed as well as the required records.. The procedure is also available separately at https://advisera.com/17025academy/documentation/test-and-calibration-method-procedure/

A question and response in Advisera Expert Community regarding  Cause 7.2.1.3 at https://community.advisera.com/topic/clause-7-2-1-3/