Toney was left out of the matchday squad by Gareth Southgate for the 1-0 defeat to Italy and, while he was included in the 23 players chosen for the Germany match, he was not called upon off the bench.
The 26-year-old had been called up for the first time by Southgate after a superb start to the season in which he netted five times in Brentford's first six league games.
And Frank says Toney must use this disappointment to fuel his performances for the Bees, telling reporters: "Of course Ivan hoped to come on the pitch.
"I think in life and football the way you get success is you can show resilience and come back from smaller setbacks.
"It is a minor setback, a minor disappointment, but you need to move forward and just prove people wrong by performing well and that's the only thing he can do.
"So it's actually relatively simple. But a little bit more difficult of course to do it day in day out. But Ivan has a strong mentality and he will do everything he can to perform well."
The 20-year-old joined Premier League side Brentford on loan this week and made his debut for the reserve side in Tuesday's London Senior Cup tie with Erith and Belvedere.
Romeo's dad was in the Park View Road stands to watch his son, who made 20 appearances for Inter Miami II in MLS Next Pro last season.
Talk of another Beckham taking the Premier League by storm has garnered plenty of attention, but Frank wants Romeo to be judged on his own ability rather than anyone else's.
"Romeo is a very good player, of course he has a name that is pretty worldwide, and big," Frank said at a pre-match press conference on Friday.
"For Romeo, he is himself. He of course has a big name. You can't compare [father and son]."
Frank drew comparisons between Michael Laudrup and his son Andreas, who the Brentford boss previously managed.
"Maybe Laudrup is also a decent player [like David Beckham]," Frank said. "I coached his son and it is important to take him as a player – not as a Laudrup, but as himself.
"Romeo is here for a reason, because we think he is a good player, and we are pleased he could make the loan deal."
Brentford B coach Neil MacFarlane praised Romeo for his display in the midweek cup tie, and Frank has challenged the youngster to do enough to earn a permanent contract.
"We're pleased to see him doing well and pleased with his performance in the last game. When you have players, either permanent or on loan, it's for a reason," Frank said.
"It's either for getting the team to perform, or to extend the loan deal and make it a permanent deal, so we just hope that he keeps progressing and makes it interesting for us."
Brentford's senior side are ninth in the Premier League and host Bournemouth on Saturday.
