Or do you just want to point out the bad and throw in the towel on the question of how it can be fixed?
Man, that's for wiser fucking people than me. I'm not going to pretend to know the best outline to split up and combine African ethnicities within contiguous borders. I studied pre-modern European history, not post-independence African geopolitics. I don't have the expertise necessary even for a rough sketch.
And honestly, I don't think it can be fixed at this point, at least not across all so-afflicted countries. The damage is largely done. In the past 60 years, institutions have been established, internal migration has intensified, nationalism cultivated, etc. Most of Africa is probably pretty stuck with the problem, and has the unenviable task of making disparate peoples cooperate within a single polity. It is possible - but it is also difficult (see: India).
Rwandan genocide was very much fueled by Belgian racial policies.
My point isn't that Africa would be a utopia if the European powers hadn't carved it up like a toddler with a birthday cake, my point is only that the borders as formed in most of Subsaharan Africa are completely arbitrary divisions which rely more on conflicting colonial interests than realities of the people on the ground.
Take a look at Nigeria if you want an example of how conflicting ethnic groups artificially forced together by an attempt of colonial powers to maintain some measure of control turns out. There's a reason most countries in Europe were either ethnically dominated empires, or ethnically homogenous nation-states - and likewise, there is a reason why European imperialists put great effort into dividing subject peoples abroad.
The ability to construct and sustain a state, or any community, is based on shared values and cultural memes.
"It tastes sweeter when you kill the watermelon with your own hands"