You have different options, none of them automatic.
One that I recommend is:
- Select the faces from the top to split the object.
- Use the command _ClayExtract.
- Inside _ClayExtract, make sure the option Copy is set to ‘No’ on the command line.
- These steps will split the object into two. If you want to one of the loops, select all the vertices from the loop you want to join (window selection) and use the _ClayWeld tool.
Another interesting solution is:
- Use the _ClayDivide command (with edge selection mode active), to create a loop of edges close to the loop you painted as red on the picture.
- You can either remove the faces created to get a small distance between both edges or use the _ClayMatch tool with the even edges to overlap positions (I do not recommend that though).
I do not know how the object is from the bottom, so these are my recommendations from what I’ve seen on your picture.
Hope it helps,