First:
2 Thess. 2:2 in older manuscripts doesn't include the word "Christ" in the text, but "the Lord". Check here
Center for New Testament Restoration
Second:
Even if there are some texts talking about "the day of Jesus Christ", like others talking about "the day of Jehovah" doesn't mean that Jesus is Jehovah. Jesus said:
Matt. 16:27 For the Son of man is to come in the glory of his Father with his angels, and then he will repay each one according to his behavior.
Actually, Jesus is the king enthroned by Jehovah in heaven, and his position corresponds to the throne of David, not to the throne of God. All Scripture speaks of Jesus being exalted by God, his superior.
Heb. 7:7 Now it is undeniable that the lesser one is blessed by the greater.
John 14:28 You heard that I said to you, ‘I am going away and I am coming back to you.’ If you loved me, you would rejoice that I am going to the Father, for the Father is greater than I am.
Jehovah has no one greater than Him:
Heb. 6:13 For when God made his promise to Abraham, since he could not swear by anyone greater, he swore by himself, 14 saying: “I will surely bless you and I will surely multiply you.” 15 So after Abraham had shown patience, he obtained this promise. 16 For men swear by someone greater, and their oath is the end of every dispute, since it is a legal guarantee to them. 17 In this same way, when God decided to demonstrate more clearly to the heirs of the promise the unchangeableness of his purpose, he guaranteed it with an oath, 18 in order that through two unchangeable things in which it is impossible for God to lie, we who have fled to the refuge may have strong encouragement to take firm hold of the hope set before us.