Maybe use a grocery bag, cut out a small hole in one of the corners of the bottom of the bag and make it into a funnel shape, pour in the chocolate that has been melted into liquid and squeeze out the heart shape.

If it's careful, it's easy to squeeze it out and use it.

If it is a big heart, then you can squeeze a layer to cool and harden, and then squeeze another layer to cool, such as these repeatedly, and finally hang the remaining chocolate pouring on the surface, shock, so that the surface is smooth. The workload is much more complicated.