I did the same last year. Pretty straightforward, really.
For the SEP & MEP it's training as required then pass an LPC. In my case the school assessed me as requiring zero training for SEP so I just did the test. I did one training flight for MEP, largely because I hadn't flown a DA42 before and I also combined it with a practice for the single pilot IR renewal.
For the FI you need to attend a standard refresher seminar and pass an Assessment of Competence. Again, I just leapt straight in and managed to scrape through. A couple of comments about how some things have changed, but no issues.
For the examiner authority they will want you to do the standardisation course and then pass the AoC as if for initial issue. I held just about every examiner authority it was possible to without being a staff examiner under the old system, and am a current multi-pilot TRE but still got zero credit.
It is nice to be back to pottering around on a nice day enjoying the view!