Learn English – which one is correct “Let this process to be completed”

Both the sentences are grammatically incorrect.

Please look at the following imperative sentence in the active voice:

Complete this process.

You use the pattern "let + object + be + past participle" to change such sentences in the passive voice as follows:

Let this process be completed.

You never use to-infinitive when you use let in the active voice or passive voice; you use the bare infinitive in the active voice and be + past participle in the passive. For examples:

Let him complete this process.

let this process be completed by him.

Let me write a letter.

Let a letter be written by me.