I will start at the end and work backwards.
QB is double entry, so your posting in 2018 to owner equity had to have affected another account - and teh hope would be that it was the expenses. If so you are all done, case closed nothing else to do.
Rules on meals and travel have changed multiple times since 2018 or even 2013 and it would be improper to expense meals for clients during time it was not allowed - and meals for yourself are hardly ever covered. The correct way to record business expenses paid from personal funds is to record the expense as coming from Owner Contribution. There is no requirement that you ever pay yourself back to recover contributions, it just affects equity. As it is you are entitled to remove every last dollar and then some (from business borrowed funds) for your own personal use so get past the idea that you somehow have to balance your equity by paying yourself back. If you put in 2 cents and sometime took out 2 cents then that ship has sailed.
If you did not expense these charges on the books then properly you can only amend tax returns 3 years back, which is what would be involved if you recorded these expenses when they occurred. I cannot advise you to simply enter one bill today for expenses from 2013-2020 and post them all as if they happened just yesterday as that would be wrong.
But back to my point, if these expenses were booked (and you received the tax benefit) even though paid out of your own pocket, then there is nothing more to do, other than clean up your chart of accounts to have 3 active equity accounts under a fourth summing only account as follows
EQUITY
<<<Owner Equity
<<<Owner Contribution
<<<Owner Draw
Post money you put in as contribution and money you take out as draw. Annually on the FIRST day of each new fiscal year move the balances from contribution and draw to the third equity account. Do it on the first so you can run an annual report of totals for the year (if you return draw to zero on 12/31 then you won't have an easy view of total for the year - even though it is of no tax consequence)
Retained earnings (your profit for the year) also goes to equity - it is a pass through item and whether you leave the money in the business or take it out also has no tax consequence in your situation.
Now the bottom line. Since you can only amend tax returns for the past 3 years, and, as per "rules of the road" the expenses should be booked as of the date they occurred, which might affect those past 3 tax returns - ask yourself this. Is the difference in increased expense enough to change your tax bracket to a significantly lower number that also would cover the added CPA costs (if you use a tax CPA). If you decrease business earnings by $500 in 2019, what affect would that have on your 2019 PERSONAL tax return? In a marginal 10% bracket that amount would be $50. Is that $50 worth the hassle of amending ALL your 2019 returns, not just business but also personal?
