Here are Bible verses that support the belief in the Trinity.
The Old Testament (OT) has many verses that teach that there only one God and God is alone (Deuteronomy 6:4, Isaiah 44:6), which is an intricate part of trinitarian belief. All scriptures that teach that God is one or alone support the belief in the Trinity.
The OT teaches about the Father, your Creator (Deuteronomy 32:6).
The OT teaches about the Son who is the Messiah. For example, Messianic Prophecy in Zechariah 14 teaches that the Lord will stand on the Mountain of Olives. And Messianic Prophecy in Daniel 7:13-14 describes the Messiah with the Ancient of Days who is the Father.
The OT teaches about the Holy Spirit (Genesis 1:2, Psalm 51:11, Isaiah 63:10-11).
Matthew 4:10 teaches that we should worship the Lord your God alone; Matthew 14:33 and 28:9 teach that the apostles worshiped Jesus; Matthew 26:42 describes Jesus praying to the Father; and Matthew 27:46 and Mark 15:34 teach that Jesus has a God.
John 5:19 teaches that the Father never works without the Son.
No human has seen God except the only Son of God who himself is God. John 1:18 TNIV, “No one has ever seen God, but the one and only [Son], who is himself God and is in closest relationship with the Father, has made him known.”
The New Testament (NT) teaches that Christ created all rulers and authorities in heaven and earth (John 1:1-3, Colossians 1:15-20).
Isaiah 44:6 says that the Lord Almighty is the first and the last, and apart from the Lord Almighty there is no God.
Revelation 21:6 says that God is the Alpha (first) and the Omega (last), the Beginning and the End.
Revelation 22:12-13 says that Christ is the Alpha and the Omega, the First and the Last, the Beginning and the End.
Matthew 1:18-20, 3:11, 12:32, and 28:19 teach about the Holy Spirit while implying that the Holy Spirit is a person.
Mark 1:8, 3:29, 12:36, and 13:11 teach about the Holy Spirit while implying that the Holy Spirit is a person.
Luke 3:21-22 shows the Father, Son, and Holy Spirit together.
John 14:14, 26; 15:26; 16:7 teach that the Holy Spirit is a person.
2 Corinthians 3:17-18 and 13:14 teach that the Lord is the Spirit of God/Holy Spirit.
The Son incarnated to die for the sins of humans (1 Corinthians 15:3) and to be an example of submitting to God and overcoming temptation (Matthew 4:10, Luke 4:8). And as I noted earlier, the Son has a God (Matthew 27:46, Mark 15:34).
All of these Bible teachings fit together. As we see from the verses above, the Bible teaches the following: there is one Lord God; the Father is God; the Son who is the one and only is God; the Holy Spirit is God; the three persons of God are one God; the three persons of God have equal authority in regards to eternal origin; the three persons of God revealed themselves in a hierarchal order to help teach humans about authority and submission; all other persons are created by the partnership of the Father, Son, and Holy Spirit.