Thank you for posting on JustAnswer. Has this seroma been lanced/opened?
Rest is likely the best option as exercise can prolong the healing process for these seroma's whether opened or left to reabsorb on their own. I recommend that if you are going to drain the seroma, that you do so only under the guidance of a veterinarian and be aware of the risks associated with opening the seroma - fly strike, abscess formation, continued drainage, serum scalding\
Did you need any further information? I think we got cut short