Tomg reply is the only way to fix this 'missing tool' issue, very time consuming and boring. If you have to do this at least setup a system that by-passes the absolute embedded path issues and address a couple of other issues.
Depending on your system: C: drive 970 Pro Nvme m.2 D: drive terabyte hard drive: Move your C:\Users\%USERNAME%\diptrace to D:\diptrace
Inside of D:\diptrace build a structure like:
model3d (diptrace)
3d (imported 3d images)
library (common libraries)
pdf (common pdf files)
archive
project
template (used for new project setup, must run git in the root of each new project to setup versioning)
library
pdf
3d
git
gerber
bom
proj-name1
.git
library
pdf
3d
git
gerber
bom
proj-name2
.git
library
pdf
3d
git
gerber
bom
--------------------------
Move all your libraries to their new D:\diptrace\library location
Use Library manager to rebuild where are libraries are
Build projects for existing projects then move all your existing PCB/Schematics into those projects or archive old projects by zipping them and moving to d:\diptrace\archive
The library and 3d path issue:
In PCB/Schematic Editor you can open a project, right click a component, click it's properties and see the library it uses and that libraries path, you could edit that to point to your new structure or:
Export the project as Diptrace ASCII, edit the project with an editor like Notepad++ configured to not change line endings, Search for C:\User and you will find your first path, do a find and replace on the path part your modifying, save the file, import the diptrace ascii after you have renamed your old project, save the imported files as the project name and move to the next project, with both PCB Editor and Schematic Editor..
(NOTE: Tomg update from schematic sounds easier!)
DipTrace as it comes from the store is not setup to be multi-user or sharable or use any type of versioning software or manage projects, the above file structure allows all this, if I contract for a project one of the deliverables is the source, with this setup it becomes a matter of zipping the project directory, exporting the git, done. Absolute directory paths are a pain but that is what we have so deal with it, build a file structure to minimize the results of absolute paths, no versioning, no project management tools, no archiving tools. If you want all that 'stuff' that are application that provide it for big bucks... $10K a seat.
Note: To run versioning you need to learn git, currently I save the versions manually but I'm working on using python to automate the system, and if Diptace would add python scripting to Diptrace we would all be better off and they would be buried in new orders.