Pumpkin or the seeds are not a proven dewormer. The OP has possible tapeworms, which is one of the hardest to get rid of. Praziquantel is the best ingredient to use for tapeworms.
That will still not work. Sorry if I confused you. Earlier when I said, 0.16 ml was just under 1/2 ml, I was way off. It is between 1/10 th and 2/10 of an ml.
Do you a syringe that measures 1 ml? It is a pretty small amount—0.16 ml for 5 pounds, so you will probably need to get a 1 ml syringe. For example, a teaspoonful equals 5 ml, and you are going to give just over 1/2 ml. Not sure how much a pea size would be.
Edited to say that 0.16 ml is...
Here it is at TSC online with free shipping:
https://www.tractorsupply.com/tsc/product/equimax-ivermectin-187-praiquantel-1403-paste-642-g?cm_mmc=SEM-_-Google-_-DynamicAdGroups-_-AllSiteTSCExtAd&gclid=Cj0KCQiAi57gBRDqARIsABhDSMof8zXVVx_ccdd-oeNhcMnwMZB86nEELESvS7rVTBRl19nFr2wcQgMaAhavEALw_wcB
You need to get Equimax horse paste which contains praziquantel and ivermectin. The praziquantel is what treats the tapeworms. Give 0.033 ml per pound of weight—for a 5 pound chicken give 0.16 ml. They sell that at TSC as well.