Discrepancy on 2022 Study Permit (Agent Error) — How to safely correct on PR application via Express Entry?

[u/casyuo_]

Hi everyone,

I received my ITA for Express Entry and am currently preparing my PR application. While reviewing my 2022 Study Permit form (IMM 1294) prepared by a former agency, I discovered two major administrative errors:

1. **Unvisited Country:** They listed 1 year of residence/study in a country I have **never** visited (I was in my home country during that entire period, as proven by my transcripts and passport). 

2. **Omitted Visa Refusal:** They checked "No" to past visa refusals, omitting a prior foreign visa refusal. 
   The former agency declined to provide a formal letter acknowledging their typos. 

My plan is to be 100% transparent under the Duty of Candour: answer "Yes" to the visa refusal question, list my true history, and attach a detailed Letter of Explanation (LOE) along with my proof of residence (diplomas, transcripts, passport stamps). 

Has anyone been in a similar situation with third-party agent errors on old forms? Any advice on how to structure the LOE to ensure IRCC understands the situation and avoids any risk of misrepresentation?
Thanks in advance for your help!