Line a baking sheet with a silicone baking liner or waxed paper.
Combine dark chocolate, coconut oil, and vanilla extract in top of a double boiler over simmering water. Stir frequently, scraping down the sides with a rubber spatula, until melted, about 5 minutes. Remove from heat and cool to room temperature, about 15 minutes.
Scoop 2 tablespoons of the melted chocolate mixture into a small bowl.
Stir blueberries and almonds into the remaining chocolate mixture. Spread on the prepared baking sheet in an even layer. Press pretzel crackers in gently. Drizzle reserved 2 tablespoons chocolate over crackers.
Freeze until firm, 15 to 20 minutes. Break gently into pieces before serving.
