Spoon condensed milk into a heatproof glass jar. Cover tightly with aluminum foil.
Place a trivet in a multi-functional pressure cooker (such as Instant Pot(R)); put jar of condensed milk on top. Fill pressure cooker with cold water up to 1 inch below the top of the jar. Close and lock the lid. Select Manual (High) pressure according to manufacturer’s instructions; set timer for 40 minutes. Allow 10 to 15 minutes for pressure to build.
Release pressure carefully using the quick-release method according to manufacturer's instructions, about 5 minutes. Unlock and remove lid. Beat dulce de leche with a spoon and let it cool completely.