A common reason a user cannot be promoted to owner of a public room is that the user doesn't have the Can create internal public rooms entitlement enabled.
Check if the user has this entitlement by following these steps:
Note: Alternatively, go to https://companyabc.symphony.com/?admin as an administrator (where "companyabc" is the name of your pod)
3. Search for the user and under Entitlements, check if the Can create internal public rooms entitlement is enabled (Figure 3):
Figure 3 Can Create Internal Public Rooms
4. If it is set to No, change this entitlement to Yes
5. Click Save
6. Return to Symphony and attempt to promote the user to the position of owner within a room. This now should succeed (Figure 4):
Figure 4 Owner
1. In Symphony, click Settings in the upper right-hand corner, then click General (Figure 1):
Figure 1 Settings/General
2. Click Go to AC Portal at the bottom of the screen (Figure 2):