POwer BI /POwer Query with General ledger data

Hi, First of all, thanks for your time. I am just want to explain myself properly. I have done many courses on LinkedIn, and other platforms when I follow the exercises that the instructor shows is really easy but when I try to apply these steps to my work I end up with many issues. For instance, I am creating a report for overtime expenses right now. the report summarizes all the general ledger accounts that are related to overtime and I want to show Actual MTD, Budget MTD, variance, Actual YTD, Budget YTD. We already created the report in excel but I want to use the power BI model I have already created which includes all the data for the Income statement and use it to create this report. I person at work usually suggests things to do and this person knows a lot but he doesn't show me. So he suggested converting my power pivot or power query model into Power BI and then using analyze excel to create the report in excel. However, I have encountered the following challenges. My data is only updated in the model until May and I need data until October. I don't know how to do that. I have refreshed the excel on the pivot table but it doesn't update I believe I need to update the model but how I can do that? second I need to create a new measure that I initially didn't need so I didn't create that new measure. The question is Where I need to create them. I feel very confused right now . If you have a tutorial or can assist I would greatly appreciate it.