Problems with Material after Merging in Modelling Section

Hey guys, before I get to the actual topic.
I’m a beginner in UE 5 Modeling and I have a pretty annoying problem.

I created and adjusted an object and meshed it in the modeling section. Only problem is it recognizes the mesh as one but all 3 individual building blocks and thus I can’t lay a texture/material without problems.

Any idea??

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