Theer or Their: How To spell?

The word Theer is misspelled against Their, a pronoun meaning "The possessive case of the personal pronoun they; as, their houses; their country."

Word contains consecutive vowels 'EI' in between alphabets th & r is misspelled as 'EE'
Wrong Spelling:  th-ee-r 
Correct Spelling:  th-ei-r 
Explore spell check of Their to spell without errors.