Try scraping this into a freshly started MMA empty notebook
c2=3;b=4;a=5;c1=6;
ComplexPlot3D[
c2 E^(-Sqrt[b] x)*Hypergeometric1F1[a/(2 Sqrt[b])+1,2,2 Sqrt[b] x]+
c1 E^(-Sqrt[b] x)*HypergeometricU[a/(2 Sqrt[b])+1,2,2 Sqrt[b] x],
{x,-10-2 I,10},PlotLegends->Automatic]
and see if you can get that to plot for you.
If it does then you can start making tiny changes, one at a time, and testing after each one to see if you can get it closer to what you actually want and still have it plot for you.
