In general, to close such "kinematic loops", you define multiple mechanism connections in the linking component.
It is not clear from your screenshot what the connections are - I will assume that your cylinder assembly ("6471K...") contains the bent sheetmetal mount "tabs", and that the component "HEAD_2_CYL" is the hockey-stick shaped connector that it is rigidly attached to the rotating "HEAD".
If that's the case, then edit the definition of the "6471K" component and:
1) add a connection of type "Rigid" where you constrain the cylinder's tab to the mount block.
2) add a 2nd connection of type "cylinder" where you constrain the cylinder's clevis pin to coincide with the hole in the HEAD_2_CYL component.