Steps : 

1.When a store is created with mixed mode store, it has siteid 1.

2.If customer creates store in mixed mode and may require to change it as Separate Store

3.iVend table RtlStore contains site id information of Store

select SiteId,* from RtlStore

4.iVend table SysNextNumber contain the next number of site id of store

select * from SysNextNumber where NextNumberid like  'Table.Store'

5.So to change it as separate store, you need to check what is last site id number in SysNextNumber for NextNumberid like  'Table.Store'  and then assign this number on RtlStore table for particular store key and Site id using SQL Query window :-

update RtlStore set SiteId='Put Next Site id' where StoreKey='Put Store key' and SiteId=1

update SysNextNumber set NextNumber='Put next number' where NextNumberid like  'Table.Store' 

6.You will be required to do this activties on other Store database so other database will get same site id of changed store

7.Generate events by updating Store description so that it could be replicated on each store by normal replication process.

it should be done with  Support Team