I would recommend burying it or putting it in moving water, such as a river.
EDIT: So I answered this first thing in the morning which was not smart, and I kinda forgot that unlike most spells, poppets are not biodegradable. I will now substitute @pomegranateandivy‘s more better answer:
“I suggest NOT doing that with most poppets. Witchcraft is not an excuse to litter. My method for getting rid of a poppet I no longer needed was to dip it in salt water, and rip the seams up to disassemble it. Then I could throw it away without worrying about causing the target harm.”