From H. W. Smyth, Greek Grammar, I §§149-188
GENERAL PRINCIPLES, ANASTROPHE, CHANGE OF ACCENT IN DECLENSION, INFLECTION AND COMPOSITION, PROCLITICS, ENCLITICS
CHANGE OF ACCENT IN DECLENSION, INFLECTION, AND COMPOSITION
176. When a short ultima of the nominative is lengthened in an oblique case
a. a proparoxytone becomes paroxytone: θάλαττα θαλάττης, ἄνθρωπος ἀνθρώπου.
b. a properispomenon becomes paroxytone: μοῦσα μούσης, δῶρον δώρου.
c. an oxytone becomes perispomenon in the genitive and dative of the second declension: θεός θεοῦ θεῷ θεῶν θεοῖς.
177. When, for a long ultima, a short ultima is substituted in inflection
a. a dissyllabic paroxytone (with penult long by nature) becomes properispomenon: λύ̄ω λῦε.
b. a polysyllabic paroxytone (with penult either long or short) becomes proparoxytone: παιδεύω παίδευε, πλέκω πλέκομεν.
178. In composition the accent is usually recessive in the case of substantives and adjectives, regularly in the case of verbs: βάσις ἀνάβασις, θεός ἄθεος, λῦε ἀπόλῡε.
a. Proper names having the form of a substantive, adjective, or participle, usually change the accent: Ἔλπις (ἐλπίς), Γλαῦκος (γλαυκός), Γέλων (γελῶν).
b. Special cases will be considered under Declension and Inflection.
Reference address : https://www.ellopos.net/elpenor/lessons/greek-accentuation.asp?pg=8