Question: If a sentence has  “if” should it b followed by a past tense verb? Not always.

The word “If” is a connecting word. It connects its adverb clause to the main clause.

If you work hard, you will get a good rank.
[subordinate clause] + [main clause]

You will get a good rank if you work hard. [The “if” clause does not have a “will” or”shall'.]
[main clause] +            [subordinate clause]

The clause carrying “If” as a connecting word shows a condition for something to happen. Therefore, it is called a conditional clause. The conditional sentence can be in the future tense.
If you hurry up, you will be able to board the train.
It can be in the past perfect tense.
If you had worked hard, you would have won the prize.

Do not be confused by an “If” sentence where the word “have” or “has” is used as a regular verb. (meaning “possess”).
If she has enough money, she will buy designer shoes. [present]
If she had enough money, she would have bought designer shoes. [past]
if she had had money, she would have bought designer shoes. [past perfect]

So, an “If” clause is used [1]  with a future tense main clause (If you wait here, I will join you soon. If he is late, we will have to go without him.)
[2] with a present tense main clause (If the sum of the digits of a number is divisible by three, the number is divisible by three. If mom comes to know, we are in trouble.)
[3] with a command (if you find the street, give me a call.)
[4] in the past tense (If she knew, she would tell you.)
[5] in the past perfect tense (If she had called, she would have been saved.) The verb “would have been” shows the future in the past.
CONTINUED…