Showing off your grades and trophies in a balanced manner, not too proud and surely not arrogant, is easy.
1. Know your stuff
Goes without being said that your interview prep has to be top notch.
Your research prior to the interview has to have been comprehensive. Armed with the knowledge, the subject matter you talk about during the interview becomes substantiated and evidence based. This means you aren't bullshitting and spouting nonsense. Very important if you don't want to look like a machine-gun racketeering aimlessly.
2. All your achievements are already in your resume and the interviewers read it already
Repeating (or rehashing) the same info from your CV/resume and duplicating the same thing over and over again is pointless and meaningless. Just like this paragraph.
For people fresh out of school and into the workforce, kids who repeat their first class honours or GPA 4.00 are considered book-smart but not street-smart. Once out of the school dates, you're in the streets. And why would a company want to hire the extreme end of the street-tard?
Don't insult their ability to read your resume.
3. Reference your abilities within the interview conversation
This is what you do. Flex your achievements by subtly referencing them in a natural conversation that has nothing to do with your grades, how you are a national swimmer, instagrammer with 350K followers or a play Apex.
As the topic goes into the job's working hours (for example), you can strike some consensus and build positive rapport.
"Oh I used to have my swim training at 5 in the mornings so I'm fine if I need to do up some prep work before everyone comes in. It's like those days I prepped for the nationals."
See that subtle flex?
"There's no problem with flexi-hours. Back when I did Insta, my friend and I did the video editing for our guest post on weekends after class."
If the interviewers are interested, they may even ask for details. You can flex your achievements even harder after that. Milk it!
"Overtime is a non-issue for me. No problem. Back in school, I volunteered for OT with the AP classes. (AP modules were optional lessons you could take in the U.S.)"
Subtle referencing for a big realisation
Make use of subtle references for a big self-induced flex
A small reference to your academic achievement is more than sufficient to pique the interviewers' interest. They are likely to relook at your resume if they need more info to connect the dots and when they do, they'll realise!
Wow! A 4.0 national swimmer, insta-influencer applying for an entry level job? Impressive! (haha, I am exaggerating. To a similar effect but not so intense!