Let me analyze this for you. To raise your urgency!
If you understand this statement from MN 56 (also other Sutta), you will know.
Just as a clean cloth rid of stains would properly absorb dye, in that very seat the stainless, immaculate the Dhamma-Eye arose in Upāli.
The stream enterer mind (Mano – cognitive mind) has been wiped clean. Their view has been straightened up (i.e. They only think about 4 noble truths if they practice).
There will be no doubt for a stream enterer (path attainer – Magga) about path, Buddha, Dhamma, Ariya-Sangha. However, it will take time for the knowledge & morality to mature (path to fruit), this maturity is not within the next 1 moment like Abhidhamma explained it. The knowledge & morality will mature:
- At most by end of his current life or
- Less than 1 day (if he has perfect morality already and very wise),
Buddha has explained this in Sutta.
Once the knowledge is matured, the 3 low fetters fall off right away. No need any teachers to declare for them.
What is the proper way for stream enterer to declare they are stream enterer?
They will say they have unshakable confidence based on direct experience on Buddha characters, dhamma characters, ariya-sangha characters, and they have a perfect morality that is loved by the other noble devotees that lead to samadhi.
Because there can’t be any other path to reach Nibbana. Everyone reaches Nibbana or Arahant or becoming a Buddha with this Noble Eightfold Steps only.
Also, There can never be any major transgression once a person has attained a path.
The other question, how can one attain a stream enterer?
They need to have a right view. Only 2 conditions for this to arise (MN 43): the words of another (another Ariya explained it for you and you hear it with your own ear) and focus attention to the source (when the teaching is being explained by the Ariya).
Also, Look SN 55.5 and SN 55.7 for 4 factors of stream enterer.
To become Ariya you need to see and know personally another Ariya as explained in MN 2 and other Sutta.
Take an educated noble disciple who has SEEN the other noble devotees (Ariya), and is skilled and trained in the teaching of the noble devotees. They’ve seen good persons (Sappurisa), and are skilled and trained in the teaching of the good persons.
Note: This is not a hearsay by someone or book reference. Also, this can’t happen even for people who study by their own the Sutta or other works.
Regarding faith, please read DN 9. If you truly understanding, you will know a stream enterer always has a sight of Nibbana (if they check). This Nibbana is here and now, not in future.
So what now?
Try to seek an Ariya or someone know one is an Ariya. Any Ariya can explain to you the complete path. So, Not only an Arahant (Perfected One) can explain to you. Even a Stream Enterer can bring a Puthujjana (common folk) to become a stream enterer.
Don’t look at the Figure, because that person is Well Known
If they are an Arahant, they should be able to bring anyone to be a stream enterer shortly. Otherwise, they might not be the real one.
Note: This doesn’t involve any single meditation practice, if there is, it is just to calm the mind to accept the teaching.