You need something to hold the capsules upright to pour the resin in and stay upright until they setup (generally overnight). These are the two ways I have found to work for me.

Modelling Clay Method versus Drilled Board Method

Modelling Clay Method - this is the simpler and low tech way but not if you are going to make a zillion. However, it is a good way to start to see if you like working with the bottles before you invest a lot of time making a better holder. Drawback, you have to reinvent the holders each time you use them.

Drilled Board Method-for many bottles at one time or to using again later. Drawback, you and the drillpress will be really good friends by the end of making a board to use. I used a drillpress instead of a simple drill so all the holes are drilled to a set depth. You need to be able to control the depth of the hole so all the capsules of the same size are set in holes of the same depth so they do not fall out easily when the board is moved but removable later after the resin has set up. This takes so time and experimenting. You need to make some test holes with various drill bits to make a hole that is comfortable -not wobbly and not snug. The individual capsule is composed of two parts when separated. You will have a short "bottle" and a "tall" bottle from the one capsule. Cool! The holes for the shorts and the talls are set at two different depths. The "bottles" need to in a hole about 1/2 the height of the "bottle" to be secure to work with. I like to have two separate boards for the shorts and talls. This makes it easier later to handle the pour amount for a specific bottle size instead of trying to switch between shorts and talls when filling the "bottles".