Set your gtmgbldir environment variable to point to the appropriate global directory.
Create a new database using MUPIP CREATE. Answer "Y" when MUPIP asks whether you wish to overwrite the existing data.
Example:
% $gtm_dist/mupip create
Database already exists on device /dev/dsk/c201d5s0
Do you wish to re-initialize (all current data will be lost) [y/n]?y
Determining size of raw device...
Raw device size is 426572K, 416572 GDS blocks
Created file /dev/dsk/c201d5s0
% $gtm_dist/mupip create