During making intention for fast in Ramadan the specific Sehri ki Dua is “Wa bisawmi ghadinn nawaiytu min shahri Ramadan” in roman means “I intend to keep the fast for tomorrow in the month of Ramadan”. Reciting Sehri dua is not mandatory during making intentions for fast but people read roza rakhne ki dua or Sehri ki dua because reciting Sehri dua shows the power of intention for fasting. May be on roza rakhne ki dua Allah will reward you with more blessings.
Sehri is a meal which we eat before keeping fast because it’s Sunnah and it wouldn’t make you feel low during fasting hours. Eating Sehri is also a blessing and people get the blessing from Allah. After eating Sehri it is necessary to make intentions to observe fast. You can make intention for fast in your heart because it’s not necessary to show your intentions through your words and if you read Sehri ki Dua or Dua for Sehri its shows the authentication of your intentions.
You can recite roza rakhne ki dua before the ending of Sehri time. Making intentions actually shows your commitment to complete the religious duties like prayers and other pillars of Islam. So similarly making intention before keeping fast is mandatory from the heart but if u recite Sehri ki dua or roza rakhne ki dua then Allah will bless you with more rewards because saying words to show your good intentions is also consider as good and it will also add in the list of your good deeds.