Hi @Jaykishan_Solanki, welcome to 
!
You can make use of the pre-formatted SILVA database, which includes all the SSU gene sequence data (i.e. 16S and 18S), from the Data resources page.
Alternatively, you can use the RESCRIPt plugin to curate the SILVA database as you'd like, as outlined here. You can also follow any of the other tutorials outlined on the GitHub page too.