There is no secret sauce for topical authority. It's not that complicated. You do not need a course for it.
What's more important is manual serp analysis, the actual ability to assess whether a keyword is rankable for your site or not. Once you know the definition of an easy keyword (UGC / forum / reddit etc. on first page OR weaker sites targeting the keyword OR authority sites not targeting the keyword) then you are good to go.
LEVEL 1: Cars (this is the topic of your site)
LEVEL 2: BMW, Mercedes, Toyota (these are the categories of your site)
LEVEL 3: BMW Repair (this is a topical cluster)
Find as many easy/rankable keywords within one cluster.
For example BMW Repair Cluster: how to fix bmw windshield, how to repair bmw bumper etc.. find them all then write articles, and interlink them.
Now keep finding more clusters within the BMW category until you run out of clusters / easy keywords.
Move on to the next category once you exhaust all articles in one category.
It is beneficial to cover a complete category before moving on since then you have topical authority for 'BMW' by itself.
Once you cover more categories you will have topical authority for 'Cars'.
P.S. You still need to build links, however, with a good topical map you need FEWER links to rank!
Good luck.