I cant install the sims 4

SoftBoyShadow​  Sorry for the late reply.  Do you still need help?  If so, please let me know whether your external drive is connected and recognized by the system, as in, you can see it in File Explorer and it has the drive letter D.  Please also let me know whether it helps to create folder on D, for example D:\Games, and choose that as the install location for Sims 4.