Which model do you have?
I wear my Fitbit Flex 2 in this.
VEAQEE for Fitbit Flex 2 Bands Jewely Necklace Stainless Steel Accessory Metal Pendant for Fitbit Flex 2 Tracker (Silvery) https://www.amazon.com/dp/B078SLRTRR/ref=cm_sw_r_cp_apa_i_fo5NCbZ7JE1M9