EXPORT YOUR TINKERCAD T-POSED CHARACTER as OBJ (Zipped file)
Create a FREE account with Mixamo and UPLOAD CHARACTER choosing the previously downloaded OBJ ZIP
ORIENT facing forward & PLACE MARKERS
LET MIXAMO DO IT'S MAGIC
It might be "buried" in the ground but go ahead and DOWNLOAD as FBX for UNITY + T-Pose
In BlocksmithXR, choose the Characters TAB and "+" and UPLOAD the MIXAMO FBX file!