[CapnScurvy]

Since your using OTC (Optical Targeting Correction), as TorpX says, take the found target radar range to the Attack Periscope station and slide out the "Attack Data Tool" by clicking the TAB at the top/right side of the screen. Setting the targets found radar range with the OTC Range Dial, and clicking the "Send" button on the Attack Data Tool will update the TDC/Position Keeper. The range dial maximum setting is 6200 yards, so any radar range over this distance need not be inputted into the TDC anyway, you're too far away to expect an accurate firing solution from the computer. The "relative bearing" of the found radar target is used on the Navigation Map to plot and plan your approach and interception of the target. The bearing has no real meaning to the TDC. There are only three things which need to be correctly inputted into the TDC/Position Keeper in order to make a firing solution.

Range to target
Speed of target
Angle on Bow of target

All can be inputted through the Attack Data Tool. Turning "on" the Position Keeper will give you a running account of where the target should be with the three pieces of information you "sent" to the computer. Remember though, the Position Keeper's account is ONLY as accurate as the information you inputted. That's why you check and double check your inputted information to make sure it's as accurate as possible. The game accounts for greater errors when the target is far away, less so the closer the target gets. Make sure you check and recheck your 3 parts of the solution for accuracy, right up to the firing time.

Since you're new to manual targeting make sure you read the information in the tutorials of OTC. The PDF "How to use Radar" should be a good start. So could the "High Realism Tutorial" that will explain the TDC/Position Keeper dials and how to plot a target on the Nav Map without having the target ship image seen on the map.

Oh, and welcome to SUBSIM!!