That’s great that you are interested in making a Spiritual Communion and using your chaplet. If you have a chaplet with 33 beads and you’re asking about Spiritual Communion, I’m guessing you have a Chaplet of the Blessed Sacrament, which was approved by St. Pope Pius X in 1911. It consists of a medal and 33 beads representing 33 years of Christ’s life on earth. You make a spiritual communion on the medal and then say a short prayer on the 33 beads.
First of all, there is nothing wrong with making a spiritual communion on the medal. There is also nothing wrong with making a spiritual communion without the medal. In short, you can make a spiritual communion as part of a chaplet or rosary (Note that the 54-day Rosary Novena has you make one as part of a Rosary,) or just on its own. It doesn’t matter, this is a private devotion, there are no “rules” as long as you’re reverent. If you say the Chaplet according to the instructions approved by the Pope, you are only making one Spiritual Communion, not 33 of them, as the 33 other prayers are not Spiritual Communions but invocations.
As for the indulgence, the original one approved by St. Pope Pius X has been abrogated, but if you were Catholic and properly disposed and had the intention of earning an indulgence, then you would still get a partial indulgence for making a spiritual communion, and in saying the rest of the chaplet might get additional partial indulgences for mental prayer, pious invocation, etc. As it appears from your profile that you are not yet Catholic, you cannot earn indulgences yet, so don’t worry about it. I’m guessing the medals with stuff about an indulgence on the back are probably old vintage medals from pre-Vatican II when the original 300 Days indulgence was still in force. Newer medals would not contain such wording.