Changing dates as a sequence

I have a list of dates in column A that look like this

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Excel doesnt recognize this as a date sequence but i need it to so that i can use the weekday formula. I have tried to change the format of these cells using the custom feature by highlighting the cells, right click, format cells, custom, then typing yyyymmdd but I just get ######### in each cell. Any solution to this? Also I cant just write over the formulas with an ascending date formula because there are some days with more than 1 date

Try this
In B1;
=DATE(LEFT(A1,4),MID(A1,5,2),RIGHT(A1,2))
Then Copy, Paste Special > Values either overtop of A or B to remove the formulas.
Does that work for you?