*_How to Count Tasbeeh_*
Whoever does Tasbeeh (dhikr) with only their right hand has been guided & achieved Sunnah
Shaykh Muhammad Nasir ad-Deen al-Albaani ﺭﺣﻤﻪ ﺍﻟﻠﻪ :
Whoever makes tasbeeh [counting subḥan Allaah as the Prophet ﺻﻠﻰ ﺍﻟﻠﻪ ﻋﻠﻴﻪ ﻭ ﺳﻠﻢ did with his fingers] with his left hand has opposed [the Sunnah]. Whoever makes tasbeeh with both of his hands like many of the people do, then he has mixed between a correct action and an incorrect action; perhaps Allaah will pardon him.
Lastly, whoever specifies his tasbeeh with only his right hand has indeed been guided and achieved the Sunnah of al-Mustafaa ﺻﻠﻰ ﺍﻟﻠﻪ ﻋﻠﻴﻪ ﻭ ﺳﻠﻢ .
[Source: Saheeh al-Adab al-Mufrad pg. 471.]