Purchase requisition deleted from system

Hi Experts,

I have created material 1234567890 and i matined min-reo-max level fix as 1000-2000-3000

Then run mrp

PR was created for 3000 nos.

Then I have created PO with HOLD.

Then level changed to 100-200-300

Run MRP

Pr was auto deleted from system and no reference found in po4500001800

Requirement:

I need to change the existing the MRP Minimum lot size-Reorder Point-Maximum stock level values,

system should consider the changed value at the time of running new pr