we have a Splunk environment using indexer clustering (9.0.0) and we have once which is acting as like DS,CM and LM, we are planning to remove LM from existing instance and we need to add to search peer is it possible.
I'd advise against putting the LM on an indexer. See https://docs.splunk.com/Documentation/Splunk/9.0.0/Admin/Configurealicensemanager#Choose_the_instanc...
See https://docs.splunk.com/Documentation/Splunk/9.0.0/Indexer/Systemrequirements#Additional_roles_for_t... for recommended places for the LM. Depending on the size and activity level of your cluster, the CM may be a good place for the LM. The best place, IMO, however, is the MC.