Generally Use past tense when you write about something that has already happened. Use present tense when you write about something that is going on now. Use future tense when you write about something that might happen in the future.
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According to the situation, you should use the past tense, future tense. As you want to indicate the happening which can be possible in the future there you should use the future tense to indicate that the happening will take place in the future.
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