The correct spelling of the phrase "dost into" is actually "dust in toe." The word "dust" is pronounced /dʌst/ and refers to tiny particles that settle on surfaces. "In" is pronounced /ɪn/ and serves as a preposition indicating location. Finally, "toe" is pronounced /toʊ/ and refers to the digits on the foot. So, "dust in toe" means that there are small particles on your toes. It's important to spell words correctly to avoid confusion and miscommunication.
The phrase "dost into" does not have a specific etymology as it is not a commonly used phrase or a single word. "Dost" is the archaic second person singular present tense of the verb "do" in Early Modern English, but "into" is a preposition that means "to the inside or interior of". It is possible that the phrase you are referring to is a combination of these words used in a specific context or sentence, but without further information, it is not clear what the intended meaning or origin may be.