Pronouns are words that replace nouns. They don't change form to indicate tense, which is the grammatical feature of verbs that shows the time of an action or state.
Verbs have tenses, such as:
* Present tense: I *walk* to school.
* Past tense: I *walked* to school.
* Future tense: I *will walk* to school.
Pronouns do not have tenses. They stay the same regardless of the tense of the verb in the sentence.
For example, the pronoun "I" remains "I" whether the verb is in the present, past, or future tense:
* I walk to school.
* I walked to school.
* I will walk to school.