Implication of hiding a short term job on my resume. Worried about HR interview. What should I do?

I worked at Company A from May 2018 to April 2021. Then I joined Company B, where I worked for four months (May 2021 to August 2021). Later, I rejoined Company A in September 2021 and have been working there since.

Since my time at Company B was short and I returned to Company A at similar pay and role, I did not mention Company B in my resume and left no employment gap. Now in my resume it appears that I worked in Company A from May 2018 to Present. I do have all relevant documents for Company B, including a relieving letter and PF account.

I have an upcoming HR round for a new company I now realize that background verification may reveal this stint due to PF records and relieving documents. I do not wish to hide anything and want to handle this the right way. I’m preparing to disclose this during the upcoming HR round with a new company. I want to ensure that this doesn’t create issues or lead to loss of opportunity. How should I handle the situation?