Generally, Baha'u'llah left everything to UHJ to lead Baha'is of the World:
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"Endowments dedicated to charity revert to God, the Revealer of Signs. None hath the right to dispose of them without leave from Him Who is the Dawning-place of Revelation. After Him, this authority shall pass to the A
ghṣán, and after them to the House of Justice—should it be established in the world by then"
Baha'u'llah, Kitabi Aghdas
From this verse it is clear what Baha'u'llah had in mind. After He passes away, First, there will be a period of Aghsan (Branches), and then after them, UHJ will have Authority. The Term Aghsan means, offsprings of Baha'u'llah.
Aghsán - Bahaipedia, an encyclopedia about the Bahá’í Faith
"All matters of State should be referred to the House of Justice, but acts of worship must be observed according to that which God hath revealed in His Book." Baha'u'llah