Sometimes just a warm bath will take care of it. Males are able to pull their own hemipenis back into it's position. Sometimes stuff getting stuck to the outside of it makes it difficult. Wash off the everted tissues and place him in a warm, not too warm, bath. A Rubbermaid tub with water just under 90 degrees will work. Leave him alone for an hour and see what happens.
If that doesn't work, try soaking the everted tissue with a sugary water solution. Basically take about a cup of water and mix in as much sugar in it as you can before the sugar quits dissolving. Then hold the swollen parts in that water. A lot of times that will cause the tissue to shrink making it possible for him to draw it back in himself.
Good luck!
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Jeff Ronne Sr
The Boaphile
Director USARK

Originator of Boaphile Plastics
The Boaphile Boa Site